This invention relates to drive axle outer end assemblies in general and is more particularly directed to a multiple disc friction brake and planetary reduction drive unit for such assemblies.
Planetary reduction outer ends are used as the final drive in axles for many heavy duty, off-highway type vehicles which are employed in the construction, logging and mining industries, as well as in farming and for mobile materials handling equipment and heavy industrial machinery. As in conventional vehicles, brake mechanisms are associated with the drive axle outer end to restrain rotation of the final drive mechanism and the wheel or sprocket driven by the drive axle outer end.
In such drive axles, the multiple disc friction brake is arranged to restrain rotation of a differential shaft input to a planetary gear reduction provided in the differential housing. In certain applications the multiple disc friction brakes engage the input shaft to the planetary reduction upstream of the shaft input to the reduction gearing. These brakes will therefore not restrain rotation of the reduction gearing for the output member driven by that gearing if the axle or input shaft breaks between the rotor friction discs and the input to the planetary reduction gearing.
The failure of a drive shaft, whether it be an axle shaft serving as an input to the final drive or a stub shaft directly driving an output member, is not an uncommon occurrence in drive axles for heavy duty equipment. It is therefore advantageous to have the brake mechanisms provided to such drive axles operative on the final reduction gearing and the output member independently of the input shaft and any shaft drive connecting the reduction gearing to the output member.
Self-contained final drive systems for axle outer ends are known where a wheel hub is driven by a planetary gear reduction unit and the multiple disc friction brake is used to stop rotation of a sun gear. In addition, certain systems are known where the multiple disc friction brakes are positioned to act directly between the ring and sun gears of the planetary gear reduction unit and the brake discs are arranged to apply a braking force directly to the carrier of the planetary gear reduction unit.
In self-contained final drive units of the above type, cooling of the multiple disc friction brake also poses a constant problem. The problem results from insufficient circulation of oil to and from the disc pack. Since the oil in such systems absorbs most of the heat energy from the discs in the pack, it will apparent that if only a small volume of oil is permitted to circulate to and from the disc pack, a serious heat problem could arise.
While the known systems operate satisfactorily in some applications, they are complex, requiring a plurality of parts, lacking in adequate cooling and also requiring much more space than is available in existing systems.